Organometallic Chemistry of the Actinides

16 Pages·2005·0.37 MB·English

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13 Organometallic Chemistry
of the Actinides
Bytheendofthischapteryoushouldbeableto:
(cid:1)
recallthatthesecompoundsareveryair-andwater-sensitive;
(cid:1)
recall that the bonding has a significant polar character, especially in the +3 state, but
that+4compounds,especiallythoseofuranium,havemorestability;
(cid:1)
recall that these compounds usually have small molecular structures with appropriate
volatilityandsolubilityproperties;
(cid:1)
recallappropriatebondingmodesfortheorganicgroups;
(cid:1)
suggestsuitablesyntheticroutes;
(cid:1)
suggeststructuresforsuitableexamples;
(cid:1)
appreciatethecontributionoftheC Me ligandinuraniumchemistry;
(cid:1) 5 5
recalltheuniquepropertiesofuranocene;
(cid:1)
appreciatetheunusualcompoundsthatcanbemadeusingimideandCOasligands.
13.1 Introduction
Althoughlackingπ-bondedcompoundsinlowoxidationstatesthatcharacterizethed-block
elements,theactinideshavearichorganometallicchemistry.Theircompoundsfrequently
exhibit considerable thermal stability, but like the lanthanide compounds are usually in-
tenselyair-andmoisture-sensitive.Theyareoftensolubleinaromatichydrocarbonssuch
astolueneandinethers(e.g.,THF)butaregenerallydestroyedbywater.Sometimesthey
arepyrophoriconexposuretoair.MostofthesyntheticworkhasbeencarriedoutwithTh
andU;thisispartlyduetothereadyavailabilityofMCl (M=Th,U)andalsobecauseof
4
theprecautionsthathavetobetakeninhandlingcompoundsofothermetals,especiallyPu
andNp.
13.2 Simpleσ-BondedOrganometallics
DuringtheManhattanproject,awiderangeofcompoundswasscreenedinthesearchfor
volatileuraniumcompoundsthatcouldbeusedforseparationofisotopesofuranium,since
UF wasnotaneasycompoundtohandle.Theleadingorganometallicchemistoftheday,
6
HenryGilman,investigatedthesynthesisofsimplealkylsandaryls,concludingthatsuch
compoundsdidnotexist,oratleastwereunstable.Eventoday,justoneneutralhomoleptic
LanthanideandActinideChemistry S.Cotton
(cid:1)C 2006 John Wiley & Sons, Ltd. ISBN: 0-470-01005-3
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210 OrganometallicChemistryoftheActinides
alkyl of known structure exists, [U{CH(SiMe ) } ], made from an aryloxide by a route
3 2 3
ensuringnocontaminationwithlithiumhalide:
3LiCH(SiMe ) +U(O-2,6-ButC H ) →[U{CH(SiMe ) } ]
3 2 2 6 3 3 3 2 3
+3Li(O-2,6-ButC H )
2 6 3
If LiCH(SiMe ) is treated directly with UCl (THF) in a salt-elimination reaction the
3 2 3 3
alkylatesalt[(THF) Li-Cl-U{CH(SiMe ) } ]isobtained.
3 3 2 3
[U{CH(SiMe ) } ]hasatrigonalpyramidalstructure,likethecorrespondinglanthanide
3 2 3
alkyls (Section 6.2.1) and also like the isoelectronic amides [M{N(SiMe ) } ] (M = U,
3 2 3
lanthanides).TherearesomeagosticU....H–Cinteractions.SimilarNpandPucompounds
[M{CH(SiMe ) } ]havebeenmade.AbinitioMOcalculationsforhypotheticalM(CH )
3 2 3 3 3
(M = U, Np, Pu) molecules also predict pyramidal structures as a result of better 6d
involvement(not5f)intheM–Cbondingorbitalsinpyramidalgeometries.
Thebenzyl[Th(CH Ph) ]hasbeensynthesizedandthepaleyellowdimethylbenzylcom-
2 4
poundTh(1,3,5-CH C H Me ) hasalsobeenreported,buttheirstructuresarenotknown
2 6 3 2 4
(andmayhavemultihapto-coordinationofbenzyltothorium).Theheptamethylthoratean-
ion[ThMe ]3− isfoundinthesalt[Li(tmeda)] [ThMe ](tmeda=Me NCH CH NMe ).
7 3 7 2 2 2 2
Thelattercontainsthoriuminmonocappedtrigonalprismaticcoordination;onemethylis
terminal(Th–C2.571A˚)whilsttheothersixmethylgroupspairwisebridgethelithiumand
thorium (Th–C 2.655–2.765 A˚). The methyl groups are, however, equivalent in solution
(NMR).
Certainsimplealkylsarestabilizedbythepresenceofeitherphosphineoramideligands,
thus:
UCl{N(SiMe ) } +CH Li→U(CH ){N(SiMe ) } +LiCl
3 2 3 3 3 3 2 3
2ThCl{N(SiMe ) } +Mg(CH ) →2Th(CH ){N(SiMe ) } +MgCl
3 2 3 3 2 3 3 2 3 2
Thesearepentane-soluble,volatiletetrahedralmolecules.Theyhaveanextensivechemistry
involving metallacycles which will be dealt with later (Section 13.6). Although MMe
4
(M=Th,U)havenotbeenisolated,thisunitcanbestabilizedaseight-coordinatephosphine
adducts,wheretheroleofphosphinesistosaturatethecoordinationsphere.Thecoordination
ofa‘soft’phosphineligandtoa‘hard’metalionlikeuranium(IV)isnoteworthy.
MCl (dmpe) +4CH Li→M(CH ) (dmpe) +4LiCl
4 2 3 3 4 2
Thesereactwithphenolformingphenoxides:
Th(CH ) (dmpe) +4C H OH→Th(OC H ) (dmpe) +4CH
3 4 2 6 5 6 5 4 2 4
Similar compounds [M(CH Ph) (dmpe) ] (stable to 85 ◦C in the absence of air) and
2 4 2
[M(CH Ph) Me(dmpe) ] have been isolated; structures of [Th(CH Ph) (dmpe) ] and
2 3 2 2 4 2
[U(CH Ph) Me(dmpe) ]confirmtheiridentity,theyhaveshortM–Ccontacts.Compounds
2 3 2
of alkyl groups like CH CH that are capable of undergoing elimination have not been
2 3
isolated.
Compounds containing one or more cyclopentadienyl-type ligands are much more
robust. (Throughout this section, C H is abbreviated to Cp; C Me is abbreviated to
5 5 5 5
Cp*;C H .CH isMeCp.)
5 4 3
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Cyclopentadienyls 211
13.3 Cyclopentadienyls
TheseareregardedasderivativesoftheC H − ligand;substitutedringsalsooccur.Some
5 5
ofthesewerethefirstorganoactinidecompoundstobereported,shortlyafterthediscovery
offerrocene.Themostimportantcompoundsareinthe+4statebutthereisasignificant
chemistryofU(+3)aswellasexamplesinoxidationstates(+5)and(+6).Onefactorthat
shouldbenotedisthatreplacingoneormorehydrogensinthecyclopentadienylringcanhave
asignificanteffectuponthestabilityandisolabilityofcomplexesmadefromthem,through
both steric and electronic effects. Thus three or four Cp ligands can be accommodated
arounduranium(IV),whereaswithCp*twoisthenorm.Inanotherexample,[UCp3]gives
no sign of reacting with carbon monoxide; [U{C H (SiMe ) } ] forms a compound that
5 3 3 2 3
canbedetectedinsolution;and[U(C Me H) ]forms[U(C Me H) (CO)],whichcanbe
5 4 3 5 4 3
isolatedinthesolidstate.
13.3.1 OxidationState(VI)
High oxidation states are not normally associated with organometallic chemistry, but a
remarkableuranium(VI)imidehasbeenmade(Figure13.1):
UCp∗(CH )Cl+Li[PhNN(H)Ph]→UCp∗(=NPh) +CH +LiCl.
2 3 2 2 4
Thereactionmaygoviaanintermediate[UCp* (η2-PhN–NPh)].Therearenof–ftransi-
2
tions in the visible spectrum, confirming its UVI-f0 character, whilst the structure of this
remarkablecompoundshowstheexpectedpseudotetrahedralgeometry;theshortU–Nbond
length(1.952A˚)confirmsitsmultiple-bondcharacterandtheU==N–Phlinkageisvirtually
linear.
NPh
U
NPh
Figure13.1
Auranium(VI)imide.
13.3.2 OxidationState(V)
RareorganoimidesU(MeCp) (=NR)havebeenmadebyoxidationofU(MeCp) (thf)with
3 3
RN (R=Me SiandPh).TheU–Nbondlengthof2.109A˚ isregardedashavingmultiple-
3 3
bondcharacter(cf.theU=Obondinuranylcompounds).
U(MeCp) (THF)+RN →U(MeCp) (==NR)+THF+N
3 3 3 2
13.3.3 OxidationState(IV)
There are three families of compounds whose structures can be regarded as derived
from a tetrahedral UX molecule with one or more halogens replaced by one or more
4
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212 OrganometallicChemistryoftheActinides
cyclopentadienyl rings; [Cp An], [Cp AnX]; [CpAnX ] (X = halogen, most usually
4 3 3
Cl). Since halogens have less steric influence than a cyclopentadienyl group, a CpAnX
3
molecule would be coordinatively unsaturated, so CpAnX actually exist as solvates like
3
CpAnX (THF) .Cp AnX areunknownforX=halogen,attemptstopreparethemresulting
3 2 2 2
inmixturesof[Cp AnX]and[CpAnX ],buttheyareknownforX=NEt andBH .
3 3 2 4
Syntheses
UCl +4KCp→[UCp ]+4KCl (C H )
4 4 6 6
UCl +3TlCp→[UCp Cl]+3TlCl (1,2-dimethoxyethane)
4 3
UCl +TlCp→[UCpCl (THF) ]+TlCl (THF)
4 3 2
Somesimilarcompoundscanbemadewithotheractinides,namely[MCp ](M=Th,Pa,
4
Np),[MCp Cl](M=Th,Np),and[ThCpCl ].
3 3
Sometimesotherstartingmaterialsareused:
U(NEt ) +3CpH→[UCp (NEt )]+3HNEt
2 4 3 2 2
Cl O
M Cl M U
O Cl
Cl
Figure13.2
StructuresofMCp ,MCp ClandMCpCl (THF) .
4 3 3 2
Structures
[MCp ] have regular tetrahedral structures whilst [MCp Cl] are analogous (Figure 13.2)
4 3
with the halogen occupying a position corresponding to the centroid of a fourth ring and
[UCpCl (thf) ]hasapseudo-octahedralstructure.
3 2
[MCp Cl]arethemostusefulofthesecompoundsasthehalogencanbereplacedbya
3
numberofgroups(e.g.,NCS,BH ,acac,Me,Ph)(Fig.13.3).
4
Cp3UMe Cp3U(OMe)
Cp3U(BH4)
MeLi NaOMe
NaBH4
NaCp
UCl4 Cp3UCl Cp3U(SCN)
MSCN (M = K, Na)
KNO3(aq) LiPPh2
[Cp3U(OH2)2]+ NO3− NaRuCp(CO)2 Cp3U(PPh2)
Cp3URuCp(CO)2
Figure13.3
SynthesisandreactionsofCp UCl.
3
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Cyclopentadienyls 213
Thereisevidenceforasignificantcovalentcontributiontothebondinginsomeofthese
actinide(IV) compounds; UCp3Cl does not react with FeCl2 forming ferrocene, whereas
MCp do(M,e.g.,Ln,U).Itappearstoundergoionizationinaqueoussolutionasastable
3
green[UCp (OH ) ]+(n∼2)cation.ThereisalsosomeevidencefromMo¨ssbauerspectra
3 2 n
ofneptunium-(III)and-(IV)cyclopentadienylcompoundsthatinaNpIVcompoundsuchas
NpCp (butnotNpIIIcompounds)thereisagreatershieldingofthe6sshellthaninanionic
4
compound like NpCl , leading to enhanced covalence in the bond. Bonds are reasonably
4
strong;themeanbonddissociationenergyinUCp hasbeendeterminedtobe247kJmol−1,
4
comparedwithavalueof297kJmol−1forFeCp .
2
Themostinteresting[MCp X]compoundsarethealkylsandaryls,[MCp R]beingmade
3 3
byreactionwitheitherorganolithiumcompoundsorGrignardreagents.
[MCp Cl]+RLi→[MCp R]+LiCl;[MCp Cl]+RMgX→[MCp R]+MgXCl
3 3 3 3
(M=Th,U; R,e.g.,CH ,Prn,Pri,Bun,But,C H ,C F ,C≡CPh,CH Ph,etc.)
3 6 5 6 5 2
Theywereindependentlysynthesizedbythreeindependentresearchgroupsatthestartof
the1970sandrepresentthefirstcompoundstohavewell-definedactinide-carbonσ bonds
(structuresforM=U;R,e.g.,Bu,CH C H CH ,etc).(See,e.g.,thepapersbyT.J.Marks
2 6 4 3
group in J. Am. Chem. Soc., 1973, 95, 5529; 1976, 98, 703.) Thermally stable in vacuo,
theyreactwithmethanol,formingMCp (OMe)andRH.Alow-temperatureNMRstudyof
3
[UCp Pri]indicatesrestrictedrotationabouttheU–Cσ bondatlowtemperatures.
3
Bonddisruptionenergiesof315–375kJ/molfortheTh–Cbondsin[ThCp R](R,e.g.,
3
CH ,CH Ph)indicatethethermodynamicstabilityofthesecompounds,comparablewith
3 2
transitionmetalalkyls(thebondenergiesare10–30kJ/mollessfortheuraniumcompounds).
Decompositiondoesnotoccurbytheβ-eliminationroute;insteadintermolecularabstraction
of a hydrogen from a Cp ligand occurs (Figure 13.4) forming RH. A stable compound
[Cp Th(µ-C H ) ThCp ]istheotherproduct(Figure13.5).
2 5 4 2 2
Th Th
H
R R
Figure13.4
DecompositionofThCp R.
3
ThesecompoundsalsoundergoinsertionreactionsofCO,CO ,andR(cid:7)NCintotheM–C
2
sigmabond,forming[Cp M(η2-COR)],[Cp M(η2-O CR)],and[Cp M(η2-C(R)NR(cid:7)],re-
3 3 2 3
spectively(Figure13.6).
Th Th
Figure13.5
Structureof[Cp Th(µ-C H ) ThCp ].
2 5 4 2 2
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214 OrganometallicChemistryoftheActinides
O
Cp3M
CO R
O
Cp3MR CO2 Cp3M R
O
R'
R'NC
N
Cp3M
R
Figure13.6
InsertionreactionsofCp MR.
3
As already mentioned, there is no UCp Cl – attempts to make it giving mixtures of
2 2
[UCp Cl]and[UCpCl ],butsomeUCp X canbemadeforexample:
3 3 2 2
[U(NEt ) ]+2C H →UCp (NEt ) +2HNEt
2 4 5 6 2 2 2 2
UCl +2NaBH →UCl (BH ) +2NaCl followedby
4 4 2 4 2
UCl (BH ) +2TlCp→UCp (BH ) +2TlCl
2 4 2 2 4 2
UCp (NEt ) reactswithROH[R=bulkygroup, e.g., [(But) C;2,6-Me C H ]:
2 2 2 3 2 6 3
UCl (NEt ) +2ROH→UCp (OR) +2HNEt
2 2 2 2 2 2
13.3.4 OxidationState(III)
A variety of syntheses are possible to these compounds, including the expected salt-
eliminationroute:
UCl +3NaCp→UCp +3NaCl(C H )
3 3 6 6
Reductionwithsodiumnaphthalenideisoftenpossible:
MCp Cl+Na→MCp +NaCl(in THF)(M=U,Th,Np)
3 3
Anunusualrouteusedforseveralofthetransuraniumelementsisamicroscalereactionof
themetaltrichlorideswithmoltenBeCp at65◦C.
2
2MCl +3BeCp →2MCp +3BeCl (M=Pu,Am,Cm,Bk,Cf)
3 2 3 2
Thecyclopentadienylproductsweresublimedoutofthereactionmixtureandcharacterized
bypowderdiffractiondata,showingtheywereisostructuralwiththecorrespondingLnCp
3
(Ln=Pr,Sm,Gd).
Similarcompoundshavebeenmadewithsubstitutedcyclopentadienylgroups;theirprop-
ertiesstronglyresemblethoseofthecorrespondingLnCp .TheunsolvatedU(C H SiMe )
3 5 4 3 3
is known to have trigonal planar geometry, as is U(C Me H) (X-ray). Lewis bases, e.g.
5 4 3
THF,C H NC,py,formpseudotetrahedraladductsUCp .L{X-ray,e.g.for[UCp (THF)]}
6 11 3 3
inthesamewaythatlanthanidesdo.Someadductsareknownwithrathersoftbaseslike
tertiaryphosphines,e.g[U(MeCp) (PMe )],thatmightnothavebeenexpectedforafairly
3 3
‘hard’metalsuchasUIII.
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CompoundsofthePentamethylcyclopentadienylLigand(C Me =Cp*) 215
5 5
Evidence from UV–visible spectra (Cm and Am compounds) and Mossbauer spectra
(Npcompounds)indicatesthatthesecompoundshaveprobablyrathermorecovalentcon-
tributionstotheirbondingthandothecorrespondinglanthanidecompounds,butarelargely
ioniccomparedwithcyclopentadienylsinthe+4state.
AnalogouscompoundsAnCp existforotheractinides,e.g.Th,Np(?),Pu,Am,Bk,Cf,
3
Cm. The thorium(III) compound is especially noteworthy, on account of the rarity of this
oxidationstate;thestructureofthesimilarTh{C H (SiMe ) } isknowntohavetrigonal
5 3 3 2 3
planargeometryaroundthorium.
3Th{C H (SiMe ) } Cl +Na/K(alloy)→Th+2Th{C H (SiMe ) } +6Na/KCl
5 3 3 2 2 2 5 3 3 2 3
These ThIII compounds are EPR-active; spectra indicate a 6d1 ground state for
Th{C H (SiMe ) } ,despitethefactthatthefreeTh3+ionhasa5f1configuration.
5 3 3 2 3
13.4 CompoundsofthePentamethylcyclopentadienylLigand(C Me =Cp*)
5 5
13.4.1 OxidationState(IV)
Compounds of the type [MCp* X ] (M = Th, U) are rather important. They owe their
2 2
importancetothefactthatalthoughthreeCp*ringscanbeaccommodatedrounduranium
in UCp* Cl,this compound cannot be made by direct synthesis (nor can MCp* ), partly
3 3
owingtothebulkoftheC Me ligands,andthe[MCp* X ]systemsareinpracticemore
5 5 2 2
readilyobtained.
MCl +2Cp∗MgBr→MCp∗ Cl +2MgBrCl (M=Th,U)intoluene
4 2 2
Halides can be replaced by suitable ligands, thus reactions with NaOMe and LiNMe
2
affordproductslikeThCp* (OMe) ,ThCp* Cl(NMe ),andThCp* (NMe ) .Li S reacts
2 2 2 2 2 2 2 2 5
forming[ThCp* (S )].Importantly,thechloridecompoundscanbealkylatedandarylated.
2 5
Eitheroneortwochlorinescanbereplaced.
MCp∗ Cl +LiR→MCp∗ (R)Cl+LiCl
2 2 2
MCp∗ (R)Cl+LiR→MCp∗ R +LiCl
2 2 2
(M=Th,U;R,e.g.,Me,Ph,CH CMe ,CH SiMe )
2 3 2 3
Theyhavetheusualpseudotetrahedralcoordination;thestructureofCp* Th(CH CMe )
2 2 3 2
reveals agostic Th....H–C interactions with the α-C–H bonds. The M–C σ bonds seem
to have a significant ionic contribution; thus ThCp* Me reacts with acetone to afford a
2 2
tert-butoxycompound.
Reactions with R(cid:7)OH, R(cid:7)SH, and R2 NH afford products such as ThCp* (R)(OR(cid:7)),
2 2
ThCp* (OR(cid:7)) ,ThCp* (SR(cid:7)) ,andThCp* (NR2 ) (R(cid:7),e.g.,Pr;R2,e.g.,Et).
2 2 2 2 2 2 2
ThecompoundsCp* Th(CH CMe ) andCp* Th(CH SiMe ) undergomostremark-
2 2 3 2 2 2 3 2
able elimination reactions to form metallacyclic complexes on heating to only 50 ◦C in
toluenesolution:
−−−−−−−−−−−
| |
Cp∗ Th(CH SiMe ) →Cp∗ Th(CH CMe -CH )+CMe
2 2 3 2 2 2 2 2 4
−−−−−−−−−−−−
| |
Cp∗ Th(CH SiMe ) →Cp∗ Th(CH SiMe −CH )+CMe
2 2 3 2 2 2 2 2 4
−−−−−−−−−−−
| |
ReactionsofCp* Th(CH CMe -CH )areshowninFigure13.7.
2 2 2 2
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216 OrganometallicChemistryoftheActinides
Cp* OR
Cp* CH
Th 3
Th
Cp* CH2But Cp* CH2But
CH
ROH 4
Cp* CH2But 50°C Cp* H Cp* H
Cp* Th CH2But heptane Cp* Th 2 Cp* Th H + CMe4
Cp*
Th
Cp*
Figure13.7 |−−−−−−−−−−−−−|
ReactionsofCp* Th(CH CMe -CH ).
2 2 2 2
Some mono(Cp*) complexes are known, reaction of MCl (M = U, Th) with
4
MeMgCl.THFyielding[Cp*MCl (thf) ],withstructuresanalogoustothe[CpLnCl (thf) ]
3 2 2 3
compounds.Thehalogenscanbereplacedwiththeisolationof[Cp*Th(CH Ph) ];thishas
2 3
a piano-stool structure with Th–C σ-bonds of 2.578–2.581 A˚. There is some interaction
betweenThandthebenzenerings,sothisisnotaclassicalη1-alkyl.
13.4.2 CationicSpeciesandCatalysts
Cationicalkylshavebeenstudiedwithprofit.Thus,inbenzenesolution,
Cp∗ Th(CH ) +[HNBun ] +[B(C F ) ]− →[Cp∗ Th(CH )]+[B(C F ) ]−
2 3 2 3 3 6 5 4 2 3 6 5 4
+NBun +CH
3 4
[Cp* Th(CH )]+ [B(C F ) ]− infacthasaveryweaklyboundanion[Th–F2.757,2.675
2 3 6 5 4
A˚; Th–C (ring) 2.754 A˚, Th–CH 2.399 A˚], so that it is an active catalyst for ethene
3
polymerizationandhex-1-enehydrogenation(Figure13.8).
IfthistypeofabstractionreactioniscarriedoutinTHF,[Cp* Th(CH )(THF) ]+[BPh ]−
2 3 2 4
isformed[Th–C(ring)2.801A˚ ,Th–CH 2.491A˚].
3
+
Cp* +
Cp* Th+ CH +H2 Cp* + Cp* Th
Cp* 3 −CH4 Cp* Th H
− Cp* + H + H2
H
Th
Cp*
Figure13.8
[Cp* ThCH ]+asacatalystforhydrogenation.
2 3
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CompoundsofthePentamethylcyclopentadienylLigand(C Me =Cp*) 217
5 5
CH
3
Th
dehydroxylated
alumina
CH
3
CH
Th 3
CH
3
partly
dehydroxylated
alumina
CH
3
Th
O
Al
Figure13.9
Surfaceboundcationicthoriumalkyls.
On alumina surfaces cationic alkyls exhibit catalytic activity, due to the formation of
coordinativelyunsaturatedspecies(Figure13.9).
13.4.3 Hydrides
Strikinghydridederivativesareformed,whichareefficientcatalystsforthehomogeneous
hydrogenationofhex-1-ene(Figure13.10):
2ThCp∗ R +4H →Cp∗ Th(H)(µ-H) Th(H)Cp∗ +4RH R,e.g.,Me
2 2 2 2 2 2
Thisremarkablethoriumcompoundisstableto80◦C.Insolutionithasrapidhydrogen
exchangewithdihydrogengas.Solution1HNMRshowsthebridgeandterminalhydrogens
are equivalent even at −90◦C. In the solid state, Th–H is 2.03 A˚ (terminal) and 2.29 A˚
(bridge);aTh–Thdistanceof4.007A˚ indicatesminimalmetal–metalbonding.IntheIR,
ν Th–H (terminal) vibrations occur at 1404 and 1336 cm−1; bridging vibrations occur at
1215,1114,844,and650cm−1.Cp* U(H)(µ-H) U(H)Cp* canbemadetoobuttendsto
2 2 2
H
H
Th Th
H
H
Figure13.10
Structureof[Cp* Th(H)(µ-H) Th(H)Cp∗ ].
2 2 2
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218 OrganometallicChemistryoftheActinides
decomposetoaUIII hydrideCp* U(H),whichcanbeisolatedandstabilizedasaDMPE
2
complex[Cp* U(H){Me P(CH ) PMe }].
2 2 2 2 2
Attempted conversion of UCp*2RCl into a hydride gives the uranium (III) compound
UCp* Cl(Section13.4.4).
2
Thehydridesarereactiveandreadilyreactwithhalogenocarbons,alcohols,andketones;
alkenesaffordalkyls.
13.4.4 OxidationState(III)
Hydrogenreductionof[UCp* ClR]givestrimericUCp* Cl(Figure13.11).
2 2
UCp∗ Cl(CH SiMe )+H →UCp∗ Cl+SiMe
2 2 3 2 2 4
U
Cl Cl
U U
Cl
Figure13.11
Thestructureoftrimeric[Cp* UCl] .
2 3
In the similar reaction with R = methyl, the organic product is CH . If the reaction is
4
carriedoutwiththeanalogousthoriumstartingmaterial,ThCp*2Cl(R)formsthethorium(IV)
compound[Cp* Th(µ-H)Cl] .
2 2
Theuraniumcompoundhasacyclictrimericstructure.Eachuraniumisindividuallyin
pseudotetrahedralcoordination.Itundergoesvariousreactions(Figure13.12).
These may be classed as straightforward substitutions using a bulky anionic ligand;
adduct formation with Lewis bases retaining pseudotetrahedral coordination; and redox.
Thephotoelectronspectrumofthealkyl[UCp* (CH SiMe )]indicatesa5f3groundstate
2 2 3
butalsothatthe5f26d1stateisonlyslightlyhigherinenergy.
[Cp*UCl]
2 2
C6H5Cl CH3Cl [Cp*2UCl2] a nd [Cp*2U(CH3)Cl]
[Cp*UCl] L
2 3
[Cp*UCl(L)] L = py, EtO, THF, PMe
2 2 3
MR
[Cp*UR] R = CH(SiMe ) ; N(SiMe)
2 32 32
Figure13.12
Reactionsof[Cp* UCl] .
2 3